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VetBooks.ir Chapter 19

Ionizing Radiation in Veterinary Medicine

Lisa Murphy

INTRODUCTION TO IONIZING Alpha and Beta Particles
RADIATION
Alpha particles are ionized helium atoms consisting of
Atoms are made up of protons, neutrons, and electrons. An two protons and two neutrons with an electrical charge
element is defined by the number of protons in its nucleus. of 12. The large size of alpha particles lowers their
When the number of protons and neutrons are balanced, the penetration capacity and makes it possible to stop them
atom is referred to as a stable isotope. Too few or too many with skin, clothing, or a sheet of paper, but they can
neutrons make the atom an unstable radioisotope or radionu- densely transfer their energy along a very short track.
clide. Radionuclides release ionizing radiation as electromag- External exposures are unable to penetrate skin.
netic waves or atomic particles as they decay to form new However, internal exposures to alpha particles can be
(daughter) radioisotopes or stable elements. These emissions extremely harmful. Damage from alpha particles is less
are able to strike an electron with enough force to strip it easily repaired compared to that from beta particles and
away from its atom, creating an ion (Rebois and Ray, 2012). gamma rays. Radon gas that occurs in homes emits
Ionizing radiation can also generate highly reactive nonionic alpha particles.
free radicals. Hydroxyl-free radicals (OH ), formed by the Beta particles are high-energy, negatively-charged
ionization of water, are responsible for the biochemical electrons that are less densely-ionizing than alpha parti-
abnormalities associated with radiation toxicity. Radiation cles though able to penetrate more deeply due to their
damage either kills cells or causes damage to molecules that lighter weight. Beta particles are stopped by thin barriers
228
increases cancer risk, particularly when DNA is involved. such as wood or metal. Radium 228 ( Ra), one of two
Other health concerns include cardiovascular effects, catar- isotopes of radium used in luminescent paints, and Iodine
131
acts, shortened lifespan, and effects on the immune and gas- 131 ( I) emit beta particles.
trointestinal systems and reproduction.
As radioactive emissions travel through cells and deposit
a concentrated amount of energy, DNA breakage and other Gamma Rays and X-rays
biological damage occur. Cells can repair much but not all
of this damage; this unrepaired damage can lead to an Gamma rays and X-rays are highly-penetrating forms
increased risk of cancer or adverse genetic effects in off- of electromagnetic radiation with unionization density
spring. Any dose of radiation could potentially cause cancer. that varies inversely with their energy (Nussbaum and
Other authors have previously covered ionizing radiation Ko ¨hnlein, 2003) and are distinguishable by their source
extensively (Henriksen and Maillie, 2003; McClellan, 2014), (Rella, 2015). Gamma rays are emitted by unstable nuclei
mainly as it pertains to human exposures and experimental via radioactive decay with a fixed wavelength. X-rays
animal data. Information regarding unintentional exposures originate outside of the nuclei. For instance, an X-ray
of animals to ionizing radiation is more limited. machine that accelerates electrons through a large voltage
Nonionizing radiation has lower energy and frequen- collides them into a metal target. Both require thick layers
of heavy material, such as lead or concrete for shielding.
cies and higher wavelengths than ionizing radiation.
Common forms of nonionizing radiation that are not cov- The cosmic radiation that astronauts and airline personnel
ered in this chapter include ultraviolet, visible light, infra- are exposed to consists mainly of gamma rays and
red, microwave, and radio frequency radiation. neutrons.

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